Monitoring of seasonal thawing in Siberia with ERS scatterometer data

Information on seasonal freeze-thaw cycle of soil and vegetation is of great interest for climate modeling and understanding the fluxes of heat, moisture and gases like carbon dioxide between the land surface and the atmosphere. Radar measurements have a great potential to provide this information, because at microwave frequencies, the dielectric properties vary considerably when going from the frozen to the thawed state. A technique was developed to retrieve the date of the transition from the frozen to thawed state based on measurements of the normalized radar cross section of the Earth´s surface by the ERS scatterometers. This technique was applied to the data obtained over Siberia for the years 1992 to 1999. The date of thawing varies locally by one month, which is about 30% of the duration of the overall thawing process in Siberia. Also, the extent of the thawed area varies considerably by up to 3×10⁶ km² from year to year for a given date. The presented results demonstrate the great potential of C-band scatterometer data for monitoring the thawing of soil and vegetation and associated processes for climatological studies